From the back of the book: "The most dangerous enemy faced by the Federation is the Klingon Empire, and yet the Klingons don't regard the Federation as their primary threat! There is much more to them.

History of the Klingons: How Kahless conquered the planet. The Old Kings who took the Klingons into space, then stranded them back on their homeworld. How the Klingons returned to the stars and conquered their mighty empire!